If a post reqeust's body contains string "%3Cmarquee+", nginx will always return 501.
Such as
request:
POST http://DOMAIN:PORT/test HTTP/1.1
Host: DOMAIN
Content-Length: 13
a=%3Cmarquee+
response:
HTTP/1.1 501 Not Implemented
Server: nginx
Date: Fri, 29 May 2015 04:30:49 GMT
Content-Type: text/html; charset=utf-8
Content-Length: 174
Connection: close
<html>
<head><title>501 Not Implemented</title></head>
<body bgcolor="white">
<center><h1>501 Not Implemented</h1></center>
<hr><center>nginx</center>
</body>
</html>